Solar radiation includes about 5% ultraviolet (UV) radiation, wavelength of which is between 200 and 400 nm. It is further classified into three regions: from 320 to 400 nm (UV-A), 290 to 320 nm (UV-B) and from 200 to 290 nm (UV-C). A large part of UV-C radiation is absorbed by the ozone layer. Scientific studies have indicated that exposure to UV-A and UV-B radiation for short period causes reddening of the skin and localized irritation, whereas continued and prolonged exposure can lead to sunburn, melanoma and formation of wrinkles. It is also reported that UV radiation causes significant damage to hair. Therefore, it is desirable to protect the skin and other keratinous substrates of the human body from the harmful effects of both, UV-A and UV-B radiation.
Further, more and more in the recent past there is evidence that it is also essential that the body is protected against the damaging effects of visible spectrum of light. Visible part of light ranges from 400 to 800 nm. It is believed that continued exposure to visible light is responsible for damaging effects on skin like erythema, pigmentation, thermal damage and free radical production (Effects of Visible Light on the Skin, Photochemistry and Photobiology, Volume 84, Issue 2, Pages 450-462, 2008). Hence in addition to protection from UV rays it is also necessary to get broader spectrum protection which includes visible light. Sunscreens or sun block agents are generally added to personal care compositions to protect the skin from harmful effects of UV radiation.
Organic sunscreens absorb a large fraction of the incident UV radiation, thereby preventing the radiation from coming in contact with the surface of the skin. They have UV absorbing sites, called chromophores, which are primarily responsible for their activity. Some sunscreens absorb UV-A radiation while some absorb UV-B radiation. The present inventors have been working for several years on providing improved methods and compounds for sunprotection purposes. One such approach has been published in Indian Patent application 2084/MUM/2006A where both UV-A and UV-B moieties are attached to a silicone backbone.
Not many compounds and compositions comprising them have been disclosed for providing protection against visible radiation in addition to UV radiation.
U.S. Pat. No. 4,381,260 (Union Carbide, 1983) discloses polymeric dyes where a group L, a divalent group, connects a chromophoric moiety to a polysiloxane moiety together by covalent bonds which imparts color to the polymer molecule. The polymeric dyes of the present invention can be used to dye natural fibers such as silk, wool, and cotton and to color plastics or used as a food dye as well as in pharmaceutical and cosmetic applications.
The present inventors have been working on the problem of providing a sunscreen that gives broad spectrum protection against both UV and visible radiation. They found to their surprise that when certain moieties generally occurring in nature e.g. hydroxyanthraquinones when attached to a silicone polymer provide not only the desired UV and visible light photoprotection but also excellent spreadability on skin and other human keratinous substrates that is essential for providing enhanced photoprotection. Further, the new polymer thus synthesized is highly amenable for further derivatisation with hydrophilic groups that enable self-emulsification of the polymer in topical products. Further, the compound of the present invention gives enhanced sun protection when incorporated in sunscreen compositions comprising conventional UVA and UVB sunscreens.
It is therefore one of the objects of the present invention is to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.
Another object of the present invention is to provide a compound that gives relatively better UV and visible light protection and at the same time provides relatively high photostability.
Yet another object of the present invention is to provide compounds that give enhanced photoprotection against both UV and visible radiation while having self-emulsifying property to enable incorporation in personal care compositions without the need for additional emulsifiers.
Yet another object of the present invention is to provide for a personal care sunscreen composition that spreads optimally on the substrate to give the desired broad spectrum photoprotection.